Parallel-stern vessel



April 22 1924.

D. w. TAYLOR PARALLEL STERN VESSEL Filed Jan.

D. W. TAYLOR PARALLEL STERN VESSEL Apg'il 22 1924.

Filed Jan. 31. 1925 3 Sheets-Sheet 2 April 22 1924.

D, W. TAYLOR PARALLEL STERN VESSEL Filed Jan. 51 1923 3 Sheets$heet 3 In ,I

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3 w uw xw NS MN Patented Apr. 22, 1924.

DAVID W. TAYLOR, OF W'A SHINGTON, DISTRICT OF COLUMBIA.

PARALLEL-STERN VESSEL.

Application filed January 31, 1923. Serial No. 618,140.

To all whom it may concern:

Be it lniown that I, DAVID WV. TAYLOR, a V

citizen of the United States, residing at lVashington, in the Districtof Columbia, have invented certain new and useful Improvements inParallel-Stern Vessels, of which the following is a specification.

This invention relates to boats, ships or other vessels which areprovided with screw propellers at the stern for moving them through thewater and is adapted and intended to cause the effective action of thepropellers in moving the vessel to be much greater than has beenpossible with the arrangement of arts on vessels heretofore in generaluse. ine of the efiects of the operation of a screw propelleris toreduce the natural or normal pressure of the water on that portion ofthe stern of the vessel directly in front of the propeller and that ofcourse tends to retard the forward movement of the vessel and thusreduces the effective action of the propeller in movingforward. Thistendency of the propeller action to suck the vessel astern is eliminatedor reduced to a minimum by the use of my present invention whichconsists in making that portion of the vessel in front of the propellerwhich would normally be affected by the suction of such shape or formlongitudinally that substantially none of the re duced pressure orsuction will-have effect in a sternward direction. Broadly it consistsina parallel stern vessel. The invention will be more fully understoodfrom the following description and claims taken with the accompanyingdrawings:

In the drawings:

Fig. 1 shows in plan the actual water lines (on sections of the surfaceby horizontal planes) of the aft portion of'an actual existingtwin-screw vessel of known type. i

Fig. 2 shows the water lines of a similar twin-screw vessel as modifiedin accordance with m invention.

Fig. 3 shows in plan the actual water lines of the aft portion of asingle screw vessel in use heretofore.

Fig. 4: shows the water lines of asimilar single screw vessel asmodified in accordance with my invention; and

Fig. 5 shows in outline a side view of a practicable arrangement of theaft part of a single screw vessel embodying my invention.

In order that the functions and advantages of my present invention maybe easily and fully understood the operation'of the propeller and itseffect in moving a-vessel 0f the ordinary tyipe now in use will be firstreferred to and explained.

A ship propeller in action produces the thrust by which a ship ispropelled by driving sternward the water upon which it acts, the thrustbeing measured by the sternward momentum impressedupon the water. Thesternwardvelocity of'the water is produced partly as a result of' excesspressure upon the sternward or driving faces of the propeller blades andpartly as a result of re duced pressure or suction upon thebacks of thepropeller blades. latter action there is a condition of reduced pressurein the water immediately forward of a propeller that is driving a ship.This reduced pressure, moreover, extends forward and outward from thepropeller and embraces the rear portion of the ship forward of thetransverse plane of the propeller. The further we goforward of thepropeller. the less the reduction of pressure. so that at a reasonabledistance in front of the propeller the reduction of pressure caused byit is negligible. The effect of the reduction of pressure acting overthe rear portion of the ship is to suck the vessel astern, as it were.thereby increasing its natural resistance. so that a part of the thrustof the propeller is absorbed in overcoming the extra resistance of theship resulting from the action of the propeller itself. This is acomplete waste of power and seriously reduces the possible efliciency ofpropulsion. 7

While the suction above referred to can be modified somewhat bymodifying propeller blades. it cannot be'materially 'reduced thus and.indeed. considering the propeller apart from. the ship, it is believedthat the larger the proportion of the thrust. due to the suction uponthe water. ahead of As a result of this the propeller, the greater theefficiency of. l

the propeller propera In considering what can be accomplished by changesin the ship itself. however. I

found that it is possible to so shape or form that portion of the shipin the region of the suction that the suction will have no materialprejudicial effect on or resistance to forward movement. The thing to beavoided is suction upon the hullin the fore and aft direction. If theside surfaces of the pertion ofthe hull in the region of suction GX tenddirectly fore and a'iter are parallel to a fore and aft line, no matterhow great the suction may be upon it, the resultantforce upon the shipdue to suction is trr verse and the fore and aft component is zero. Inpractice the suction in front or" a propeller decreases steadily andfairly rapidly at successively greater distances forward from the planeof the blades and is virtually negligible for a propeller not too deeplyimme..s..d at a distance from the propeller center of about twodiameters oi the propeller. It therefore follows that it the aft part ofthe hull is so shaped that the portion which is submerged when underway,although having sh ape in transverse planes, has side surfaces on linesparallel to the center line for a distance "forward of the propellerequal to about two diameters of the propeller. the harmful suction willbe virtually nullified. However even where the rear portion of the hullhavingits sides parallel to fore and att line extends for a lessdistance forward the rearward suction will still be materially reducedthus securing the benefits of the present invention. the amount of thereducth'in depending upon the extent of the fore and att portion hav ingthe parallel sides.

In the case of twin-screw vessels there are no serious practicaldiiliculties in the wav of making the rear underwater portion oi thehull forward of the plane oi the propellers practically fore and aft. i.e. a true parallel stern. For single screw vessels considerations ofstrength render it inadvisable to shape the rear portion of the hullside surfaces exactly parallel to a fore and aft line: but by giving aslight divergence to the water lines in this part of the ship at a smallangle. preferably not exceeding 5. my invention may be applied to singlescrew vessels with but slightly less effectiveness than in twin screwvessels. In pra tice. ships are now usually built. it. is the waterlines near the surface which diverge at large angles to the fore and aftline, as compared with those well under water. and the greatest benefitwill follow from the reduction of these water line angles to zero or toa small angle.

In order to make clear the meaning of the drawings by inspection.descriptive words and abbreviations and numbers have been placed on eachfigure the letters V7. L. being used to indicate waterline and thenumeral with an apostrophe to indicate feet. By comparing Figures 1 and2 it will be seen that in applying my invention to the vessel the deckline is not changed. Below the deck line the horizontal lines are drawnin gradually until the most radical change in the angle to the fore andaft line is at the actual water line of the vessel underway menace asindicated in Figure 2 labeled Load water" line 236. Below that line thechanges are much less radical as the keel is approached. The lines ofFigures 1 and 2 indicate a vessel with a thick stern post where therudder is of substantial thickness and carries on the water lines abai'tthe stern post as indicated by the dotted lines in Figure 2 abaft thesix-foot and twclve-foot water lines.

The dotted lines 11 in Figures 1 and Q indicate the transverse plane ofthe propellers and a dotted line 12 in Figure 2 indicates the transversevertical plane of the vessel where the drawn in water lines forming theparallel portion commence to curve outwardly from the central fore andaft line towards their normal positions. It will be noted by comparisonof Figures 1 and 2 that the water lines above the propeller and parallelportion and in front of it and even above the actual water line underload are drawn in to a. material extent for structural reasons.

It will be observed by inspection of Figure a that in applying theinvention to a single screw vessel the water lines of that portion ofthe vessel directly in front of the propeller are not exactly parallelto a fore and aftline but diverge at very small angles increasing fromthe lower edge to an angle of about 5 at the upper portion. This resultsin comparatively little change from the normal water lines near the keelbut there is a radical change near the actual load water line of thevessel. As in the case of the twin screw vessel however there is littleor no change at the upper deck. In Figure 3 the dotted lines 13represent the propeller shaft bossing. 14: represents the stern post andthe rudder post of the ordinary vessel. The propeller is mounted andoperates between stern post 14 and rudder post 15.

lnapplying the inv-nliion to a single screw vessel it is desirable.although not necessary, to carry the stern overhang a little furtherbacl: than is usual in order to make it strong enough to carry withsafety a rudder of the balanced spade type which is supported entirelyin the hull above it as illustrated in Figure 5. This obviates thenecessity for fitting the rudder post behind the Screw propeller andreduces the strain on the stern of the ship below the stern tube.

Figure 5 shows in outline one desirable general arrangement by whichthis may be done. It will be noted from an inspection oi Figs. 4 and 5that the upper part of the hull in the rear of the stern post 18 issupported by what may be called a shelf 19 which is in a straighthorizontal plane at the 20 water line and which forms the bottom surfaceof that portion of the hull and which is rigidly connected to andsupported by the portion of the hull next forward. This shelf provides afiat downwardly facing surface and carries the bearings 24 which supportthe rudder and it adds strength to the upper part of the hull. In thiscase the angle of divergence of the 24 water line from the fore and aftline is reduced from about in the usual type of vessel illustrated inFigure 3 to about 5 in the one embodying my invention as shown in Figure4:. This angle is so slight.

even at the water line that the vessel has a substantially parallelstern. The propeller 20 is below the shelf and between the stern post 18and the rudder 25 as shown in Fig. 5.

It will be seen by reference to Figure 4 that the 20 water line 21 belowsaid shelf terminates at the stern post 18 and from that pointforward isat a very slight angle to the center fore and aft line until at thedotted line 22 it curves outwardly and joins the 20 water line above theshelf at the point 23. There are thus narrow side sections of the shelffrom the stern post 18 to the points 23 on opposite sides. Since aparallel stern vessel such as described above greatly reduces thesternward suction on the vessel and thus secures the advantages of myinvention whether the propeller is mounted on the central fore and aftline or at one side my invention is not limited to any particularnumb-er of propellers and the reference to propeller in the claims isintended to means one or more.

Having thus described the invention what is claimed as new and desiredto be secured by Letters Patent is:

l. A propeller operated vessel so shaped that the corresponding port andstarboard water lines of the submergedportion immediately forward spacedapart laterally a short distance sufficient to accommodate the sternpost or other necessary structural features between them and extendingforward substantially of the propeller are.

parallel to a fore and aft line for a material distance from thepropeller and then diverging on outward curves.

2. A propeller operated vessel so shaped that the corresponding port andstarboard water lines mediately forward of the propeller are spacedapart laterally, a short distance sufficient to accommodate the sternpost or other necessary structural features between them and extendingforward substantially parallel to a fore and aft line for tance from thetransverse center line of the propeller approximately equal to twice thediameter of the propeller and then diverging on outward curves.

3. A propeller operated vessel so shaped that the corresponding port andstarboard water lines of the submerged portion immediately forward ofthe propeller are spaced apart laterally a short distance sufficient toaccommodate the stern post or.

other necessary structural features between them and extending forwardat an angle to a fore-and aft line not greater than approximately 5 fora materialdistance from the propeller and then diverging on outwardcurves.

1. A propeller operated vessel so shaped that the corresponding port andstarboard of the submerged portion ima dis water lines of the submergedportion immediately forward of the propeller are spaced apart laterallya short distance sufficient to accommodate the stern post or othernecessary structural features between them and extending forward at anangle to a fore and aft line not greater than approximately 5 for adistance from the center transverse line of the propeller approximatelyequal to twice the diameter of the propeller and, then diverging onoutward curves. 7

In testimony whereof I hereunto afiix my signature. 1

DAVID W. TAYLOR.

